There are reinforced tornado shelters in more than 100 schools across Oklahoma, excluding the two that were devastated by a Tornado earlier this week in Moore, Okla., an emergency-management official said.

As authorities search the rubble in Moore for possible survivors and bodies, among the unanswered questions is how everyone at Briarwood Elementary School survived while several students died at Plaza Towers Elementary School. Both schools were destroyed when an EF-5 twister with winds of at least 200 mph killed 24 people Monday and injured hundreds more. Six people are unaccounted for.

Some people believe those at Briarwood were more fortunate because of the school's construction.

Each grade at Briarwood is organized into four pods with a few classrooms in each pod. An opening to the outside runs through the center of the pods. Teachers said that when the walls and ceilings collapsed, they crawled through that open area and children were passed over the rubble.

Plaza Towers Elementary is more of a traditional school building with a long line of classrooms, all under one single roof. When the school collapsed, the roof and walls piled on top of one another, making it difficult for people to crawl to an outside space.

Both schools had practiced tornado drills but neither had a safe room, which could have potentially saved lives.

"You have limited amount of funds that are based on disasters we've had in the past that are used for mitigation measures and when you have limited number of funds, then you set priorities on what schools that you do want to ask for," Oklahoma Director of Emergency Management Albert Ashwood said.

More than 100 schools across Oklahoma have safe rooms and the state hopes to increase those numbers, Ashwood said.

"We're going to be looking at trying to up that number and try to get more safe rooms across schools across the state, the entire state," he said.

Metal safe rooms can be built above ground or underground and undergo rigorous tests to make sure they can sustain winds up to 250 mph. Researchers have conducted test on safe rooms to show they can withstand being hit by a car.

Moore has been trying to get federal money to subsidize residents who want to buy safe rooms. The city expressed its frustration in February on the city website, saying, "We've found that the FEMA requirements and their interpretations seem to be a constantly moving target, more so with the new wrinkles."

"If you don't have disasters, you don't have additional money for mitigation for safe rooms, but without disasters there's not a set funding source just for safe rooms," Federal Emergency Management Agency Director Craig Fugate said.

Alabama is the only state that requires all new schools to have safe rooms for students.

Many homes in the Midwest, known as Tornado Alley, don't have basements because of loose clay soil or flooding conditions. An indoor safe room might be the best option for families and schools.

"There are above-ground and below -round storm shelters that offer near absolute occupant protection from the worst-case tornado," said Ernst Kiesling, professor of civil engineering at Texas Tech University in Lubbock.

Meanwhile, authorities have searched each damaged home at least once, and the goal is to conduct three searches of each location just to be sure. Moore Fire Chief Gary Bird said he was "98 percent sure" there were no more bodies or survivors in the rubble.

Classes at Moore public schools have been canceled for the remainder of the school year but graduations will continue as planned.

Secretary of Homeland Security Janet Napolitano will travel to Oklahoma later today to meet with state and local officials and ensure that first responders are receiving the assistance they need.